Solar String Size Calculator: Cold Voc, MPPT Range, and Current Limits
Last reviewed August 2, 2026. Verify every entered rating against the exact module and inverter or controller manuals and applicable electrical requirements.
Direct answer: Enter exact module and inverter/controller ratings plus design cell temperatures. The result checks series voltage, the MPPT operating window, and current assigned to each tracker; it is not a complete electrical design.
Inputs
Results and limit checks
Results appear here after you click Calculate. Enter your values, then compare the result with the interpretation notes below.
Interpretation
A pass means only that the entered values fit the tested arithmetic limits. A warning identifies an untested optional limit. A fail names the exact input or tracker assignment that caused it. Recheck the result whenever the module model, equipment model, temperature basis, number of strings, or tracker assignment changes.
Formula or method
Cold-corrected Voc = Voc × [1 + coefficient × (25°C − low cell temperature)]. Hot-corrected Vmp = Vmp × [1 − coefficient × (high cell temperature − 25°C)]. Maximum and minimum series counts use the equipment voltage limits. Tracker Imp is module Imp × assigned strings × bifacial factor. Adjusted tracker Isc also applies the Isc safety and manufacturer factors.
Assumptions and limitations
- Temperature coefficients are entered as positive magnitudes; the calculator applies the direction shown above.
- Equal modules are assumed within each string. The tool does not model mismatch, optimizer-specific rules, conductor ampacity, overcurrent protection, rapid shutdown, grounding, connectors, or code.
- Roof orientation and shade are layout considerations, not current-limit inputs here.
- The exact module and inverter/controller manuals govern absolute voltage, MPPT, per-input, and per-tracker rules.
Worked example
With the defaults, ten modules are checked against a 600 V absolute limit and a 120–480 V MPPT window. Four strings are assigned 2,2 across two trackers; each tracker is checked separately against operating-current and adjusted short-circuit-current limits.
Sources
- Sandia PV Performance Modeling Collaborative: DC module IV characteristics: supports using module ratings and temperature-sensitive models for planning; exact equipment datasheets govern safety limits.
- U.S. Department of Energy home solar guide: supports checking site conditions, system design, equipment, permitting, and installer documentation before installation.